1. Field of the Invention
The present invention relates to an integrated coal gasification combined cycle plant for combined power generation using coal as fuel, and more particularly, relates to gas processing at a startup stage in a flue-gas-desulfurization-type integrated coal gasification combined cycle plant.
This application is based on Japanese Patent Application No. 2004-188887, the content of which is incorporated herein by reference.
2. Description of Related Art
Heretofore, an integrated coal gasification combined cycle (hereinafter referred as “IGCC”) plant has been known. In this IGCC plant, a produced gas obtained through gasification at an early stage (hereinafter referred to as an “early produced gas”) when the operation of the IGCC plant is started does not satisfy the conditions for use as fuel for a gas turbine due to, among other factors, the low calorific content, and hence the early produced gas must be processed in a gas processing system such as a flare system before it is supplied to the gas turbine. The processing of the early produced gas is called startup gas processing.
In a flue-gas-desulfurization-type IGCC plant, since an early produced gas processed by a flare system or the like does not pass through a gas clean-up system, the gas contains a large amount of a sulfur component. Accordingly, when the early produced gas is directly processed by a flare system, although it takes a relatively short period of time (approximately 2 to 3 hours in general), a relatively high concentration of the sulfur component is emitted into the atmosphere, which is undesirable.
When an early produced gas which satisfies predetermined conditions starts to be supplied as a fuel gas to a gas turbine, exhaust gas from the gas turbine is made to pass through a flue gas desulfurization (FGD) equipment which performs desulfurization and is then exhausted into the atmosphere, thereby causing no environmental problems at all.
One technique in the related art for processing the above-described early produced gas is, for example, to use a system in which the early produced gas is received in a H2S combustion furnace and is then removed in a wet-type desulfurization tower used for an off-gas. In this case, the waste heat is recovered as re-boiler steam (for example, see Japanese Unexamined Patent Application Publication No. 9-268904).
The flue-gas-desulfurization-type IGCC plant described above suffers from the problem that, since the sulfur component contained in the early produced gas, which is produced by gasification at an early stage of the plant startup, is processed without any pretreatment, the sulfur component is emitted into the atmosphere. Hence, in consideration of recent environmental concerns, there have been demands to solve the atmospheric emission problem of the sulfur component using appropriate gas processing, even though the emission lasts for a short period of time at the startup stage, and to improve the environmental compatibility of IGCC plants at a low cost.
In the structure disclosed in the above Japanese Unexamined Patent Application Publication No. 9-268904, there has been a problem in that the volume of the off-gas wet-type desulfurization tower is increased, although it was originally small.